Push-pull amplifier



Jan. 23, 1934. LAPQRT PUSH-PULL AMPLIFIER Filed Feb. 28, 1931 0' o on 0.00000 0 INVENTOR Edmund ,4. Lei 20H? WETNESSES i iou -74;

ATTORNEY Patented Jan. 23, 1934 UiNi'iiih STATES PUSH-PULL AMPLIFIER Edmund A. Laport, Springfield, Mass, assignor to Westinghouse Electric & Manufacturing Company,

a corporation of Pennsylvania Application February 28, 1931. Serial No. 518,923 r 4 Claims.

My invention relates to high-power radio-irequency amplifiers and particularly to an improved means for neutralizing a push-pull amplifier.

One circuit for neutralizing a push-pull am- 5 plifier is shown in Ballantine Patent No. 1,560,332.

It has been found in practice that, when the connections are made as shown by Ballantine, the neutralizing leads are so long that it is difiicult to neutralize the amplifier at high frequencies.

My invention consists in so arranging a pushpull neutralizing circuit that the neutralizing leads are very short. As a result, the amplifier may be readily stabilized at very high frequencies.

In practicing my invention, I connect the anodes of the vacuum tubes to the tank circuit by means of the cross-connections which were formerly employed as neutralizing connections. While this makes the anode connections longer than when the other arrangement is employed, this is not objectionable because the grid leads are the only ones that make the circuit unstable if they are too long. The grids of the tubes are then connected to the proper points for neutralization by means or" the leads which were formerly employed to connect the anodes to the tank circuit.

Other features and advantages of my invention will appear from the following description, taken in connection with the accompanying drawing in which: a

Figure 1 is a circuit diagram of an amplifier constructed in accordance with my invention, and

Fig. 2 is a schematic diagram in plan view of the apparatus and electrical connections of the amplifier shown in Fig. 1.

Referring to the drawing, the amplifier comprises two vacuum tubes 10 and 11 which have their cathodes electrically connected through a conductor 12. The cathodes are preferably 4 grounded. The input circuit for the amplifier consists of a resonant circuit 13 which includes an inductance coil 14 and two condensers 15 and 16 connected in series. The cathodes of tubes 10 and 11 are connected, through a conductor 1'7,

to the circuit 13 at a point betwen the condensers 15 and 16.

The grid 18 of the tube 10 is connected, through a conductor 19, to the junction point of the inductance coil 14 and the condenser 15. The grid 20 of the tube 11 is connected, through a conductor 21, to the junction point of the other end of the inductance coil 14 and the condenser 16.

A lead 22, connected to the mid-point of the inductance coil 14, is connected to the negative ter- '55'minal of a grid-biasing source of potential (not shown). The energy to be amplified is supplied through an input coil 23.

The output circuit of the amplifier comprises a resonant circuit 24 which is known as the tan circuit. The tank circuit 24 consists of an inductance coil 25 and two condensers 26 and 27 connected in series. The conductor 28, 1 connecting the condensers 26 and 27, is connected to the cathodes of the tubes 10 and 11 through a conductor 29.

The junction point of the inductance coil '25 and the condenser 26 is connected, by means of a cross connection 30, to the anode of the tube 11. The junction point of the inductance coil 25 and the condenser 27 is connected to the anode of 7 the tube 10 through a cross connection 31. It will be noted that this circuit differs from the circuit shown in the above-mentioned Ballantine patent, in that, in Ballantines circuit, the cross connections include neutralizing condensers In accordance with my invention, the grid 18 of the tube 10 is connected, through a short conductor 32 and a neutralizing condenser 33, to the junction point of the inductance coil 25 and the condenser 26. The grid 20 of the tube 11 is likewise connected, through a short conductor'3 and a neutralizing condenser 35, to the junction point of the inductance coil 25 and the lower condenser 27.

Plate voltage is supplied to the tubes 10 and 11 through a conductor 36. The amplified energy is transmitted to the radiating or other work circuit through a secondary winding 37.

The advantage of the connections described above is clearly shown in Fig. 2 where the rela- Q tive sizes and positions of the amplifier units are shown. As indicated in Fig. 2, the tank-circuit condensers 26 and 27 occupy more space than the vacuum tubes. It is mainly because of the large F size of these condensers that it has been difficult 5 in the past to avoid long neutralizing leads.

I have overcome the diificulty by placing condenser 26 close to tube 10, by placing condenser 2'7 close to tube 11 and by then connecting the grids of tubes 10 and 11 to the neutralizing condenser plates 33 and 35, respectively, by means of the short leads 32 and 34.

It will be noted that one plate or condenser 27 acts as one plate of the neutralizing condenser 35. Neutralizing condenser 33 is formed in a similar manner.

The neutralizing circuit is then completed by means of cross connections 30 and 31. Connection 31 connects the plate of tube 10 to the grid of tube 11 through the neutralizing condenser 35 and the short lead 34. Cross connection 30 connects the plate of tube 11 to the grid of tube 10 through the neutralizing condenser 33 and short lead 32.

The dimensions of the apparatus illustrated in Fig. 2 are approximately as follows:

Diameter of the plates of condensers 26 and 27-three feet;

Distance from the front condenser plate 38 to the back condenser plate 39five feet.

In practice, the vacuum tubes employed have been those designated as UV862 tubes. In Fig. 2, two tubes of this type mounted in a vertical position are illustrated diagrammatically. These tubes have a diameter of approximately 8 inches and a height of about five feet.

It will be apparent to those skilled in the art that the anodes and neutralizing condensers need not be connected exactly at the junction points of the inductance coil and a condenser. For example, either the anode of the tube 11 or the condenser 33, or both, may be connected to a point on the coil 25 half Way between the end of the coil and the mid-point. The term junction point in the claims includes all such modifications of the circuit.

The term two vacuum tubes in the claims also includes groups of parallel-connected tubes arranged in push-pull.

Various other modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and are set forth in the appended claims.

I claim as my invention:

1. An amplifier including two electron tubes connected in push-pull and having a cathode, a grid, and an anode and having an output circuit, said output circuit including a resonant circuit comprising capacity and inductance units, the mid-point of one of said units being connected to said cathodes, said anodes being connected to said resonant circuit at opposite sides of said mid-point by means of cross-connections, and a neutralizing condenser connected between the grid of each tube and the side of the resonant circuit which is connected to the anode of the opposite tube.

2. An amplifier including two electron tubes connected in push-pull and having a cathode, a grid, and an anode and having an output circuit, said output circuit including a resonant circuit comprising capacity and inductance units, the mid-point of one of said units being connected to said cathodes, said anodes being connected to said resonant circuit at opposite sides of said midpoint by means of cross-connections, and condenser plates positioned adjacent to and spacially inseparablefrom said capacity unit, the grid of each tube being connected through one of said condenser plates to that side of the resonant circuit which is .connected to the anode of the opposite tube.

3. An amplifier including two electron tubes connected in push-pull and having a cathode, a grid, and an anode and having an output circuit, said output circuit including a resonant circuit comprising an inductance coil and two condensers connected in series, said cathode being connected to a point on said resonant circuit intermediate said two condensers, said anodes being connected to said resonant circuit at opposite sides of said intermediate point by means of cross-connections, and condenser plates ,positionedadjacent to andspacially inseparable from those plates of said condensers which are connected to said inductance coil, the grid of each tube being connected through one of said condenser plates to that side of the resonant circuit which is connected to the anode of the opposite tube.

4. An amplifier including two electron tubes connected in push-pull and having a cathode, a grid, and an anode and having an output circuit, the mid-point of said output circuit being connected to said cathodes, said anodes being connected to said output circuit at opposite sidesof said mid-point by means of cross-connections, and a neutralizing condenser connected between the grid of each tube and the side of the output circuit which is connected to the anode of the opposite tube.

EDMUND A. LAPORT. 

